An Evaluation of Carbon Dioxide Flooding

Abstract

SPE Member Summary Laboratory core displacement tests were made to better understand the effects of miscibility, swelling and viscosity reduction on oil recovery by CO2 flooding. Also, certain field applications were reviewed to assess performance of CO2 flooding under miscible and immiscible conditions. Achieving miscibility is shown not to be essential to recovering incremental oil since viscosity reduction and oil swelling can also be very important. Recommendations are offered as to how best to pilot test CO2 flooding in the field to obtain reliable performance data. performance data. Introduction Miscible flooding, in particular CO2 miscible flooding, is regarded as the most promising process for enhanced oil recovery. The industry interest in CO2 flooding is evidenced by the large number of field applications which have been initiated in the last two decades. Additional field applications are certain to be carried out when further CO2 sources are found. All major petroleum industry, university and government research centers have projects related to CO2 flooding. Mungan has compiled a comprehensive review of CO2 flooding. Basically, CO2 flooding has been studied in the laboratory or applied in the field in the following modes: CO2 stimulation, continuous CO2 injection, the CO2 slug process, simultaneous injection of CO2 and water, alternating injection of CO2 and water, injecting H2S or SO2 with CO2 to lower the minimum miscibility pressure (MMP), injecting CH4 with CO2 to take advantage of gravity stabilization, flue (combustion) gas injection, injecting LPG and CO2 mixtures, and LPG followed by CO2. With two exceptions, the CO2 flooding process normally involves the injection of essentially pure CO2 initially, followed by a period in which the CO2 is alternated as small slugs with another fluid, and terminates with the injection of the principle driving fluid, which could be either water or gas. One exception is the carbon dioxide stimulation process, which is carried out in producing wells and process, which is carried out in producing wells and is a stimulation technique very similar to a "huff-and-puff" scheme. This process involves CO2 injection only. The other exception occurs in reservoirs which have such low pressure that they must initially be pressurized to MNP prior to the injection of CO2. Normally, such pressurization is by injection of water. P. 113